1. Field of the Invention
The present invention relates to a motor used for rotating a disc-like medium, particularly to a revolving-field type motor, and more particularly to a motor having a characteristic structure in an armature. Further, the present invention relates to a rotating apparatus of a disc-like medium using the motor mentioned above, for example, a disc apparatus.
2. Description of the Related Art
A revolving-field type motor of an outer rotor type is generally used for a motor used for rotating a disc-like medium due to a smooth rotation and a simple structure. Accordingly, a description will be given of a prior art on the basis of an exemplification of an outer rotor type motor.
In this case, the disc-like medium indicates a concentric disc-like medium having a center hole, and for example, means a medium such as a floppy disc, an MO, an MD, a PD, a CD (ROM, R and RW), DVD (ROM, R, RW and RAM) and the like as well as an old record (LP, EP and the like) disc. These mediums collectively means a disc simply in the following description. Further, since an object is to rotate the disc, the medium is called as the disc without relation to a matter whether or not the disc is received in a jacket.
At first, a description will be given below of a radial gap motor and an axial gap motor, as a conventional motor technique. FIG. 17 is a perspective view of a conventional radial gap motor, and FIG. 18 is a cross sectional view along a line X—X in FIG. 17. A description will be given of a structure of the conventional radial gap motor on the basis of the perspective view in FIG. 17 and the cross sectional view in FIG. 18.
Reference numeral 10 denotes a pole, which corresponds to a laminated iron core pole formed by laminating a plurality of silicon steel plates for preventing a eddy current. Reference numeral 46 denotes a coil, which is wound around the pole 10 and to which a driving current is applied. Reference numeral 61 denotes a magnet, which is arranged so as to oppose to the pole 10. Reference numeral 13 denotes a turn table on which the disc is mounted so as to rotate. Reference numeral 21 denotes a bearing, which holds a center shaft of the turn table 13. Reference numeral 15 denotes a chucking unit for mounting the disc to the turn table 13, which is generally structured such as to determine a center position of the disc by a chucking ball 16 so as to closely contact the disc with the turn table 13.
Next, FIG. 19 is a schematic view describing a rotating operation of the structure shown in FIG. 17. In FIG. 19, a magnet 61 of the radial gap motor is magnetized so that an S pole and an N pole are respectively distributed in an inner peripheral side and an outer peripheral side. When applying the driving current to the coil 46, the pole 10 is magnetized in accordance with a screw law. In the manner mentioned above, a repulsive force or a suction force is generated between a magnetic pole of the pole 10 and the magnet 61. In this case, the structure is made such as to alternately generate and switch the repulsive force and the suction force generated between the magnet 61 and the coil 46 as shown in FIG. 19 by controlling a current applied to a plurality of coils 46 and a timing thereof, thereby continuously generating a propelling force in a fixed direction and rotating the turn table 13 corresponding to a rotor magnet.
Next, a description will be given of a axial gap motor corresponding to another prior art. FIG. 20 is a perspective view of a conventional axial gap motor, FIG. 21 is a cross sectional view along a line Y—Y in FIG. 20, and FIG. 22 is a schematic view describing a rotating operation of the structure shown in FIG. 20. In the perspective view in FIG. 20 and the cross sectional view in FIG. 21, reference numeral 47 denotes a coil to which a driving current is applied. The structure is made such as to form a plurality of coils 47 on a printed circuit board and thereafter coating by an insulative material such as a resin or the like so as to be integrally formed on a coil circuit board 49. Reference numeral 62 denotes a magnet, which is arranged in parallel to the coil circuit board 49.
Reference numeral 51 denotes a ferromagnetic yoke mounted so as to be closely attached to the magnet 62. Reference numeral 34 denotes a turn table mounting the disc thereon so as to rotate, and reference numeral 22 denotes a bearing holding a center shaft of the turn table 34. Reference numeral 15 denotes a chucking unit, which determines a center position of the disc in the chucking ball 16 and closely attaches the disc to the turn table 34.
Next, a description will be given of a rotating operation of the axial gap motor on the basis of FIG. 22. As mentioned above, the magnet 62 is magnetized so that the S pole and the N pole are respectively distributed in the upper surface side and the lower surface side. Further, FIG. 23 is a view showing a magnetization distribution of the magnet. As shown in FIG. 23, the magnet 62 is magnetized so as to be separated into a plurality of areas in a circumferential direction. Then, since the magnet 62 is held between the turn table 34 and the yoke 51, as shown in FIG. 21, a magnetic flux is generated in an axial direction (a direction of a rotary shaft of the motor). Further, when applying the driving current to the coil 47, a magnetic flux due to the coil current is generated in accordance with a screw law.
In the manner mentioned above, the repulsive force or the suction force is generated between the magnetic flux due to the coil current and the magnet 62. In this case, by controlling the electric current applied to a plurality of coils 47 and the timing thereof, it is possible to alternately generate and switch the repulsive force and the suction force generated between the magnet 62 and the coil 47 as shown in FIG. 22 so as to continuously produce a propelling force in a fixed direction, thereby rotating the turn table 34 corresponding to the rotor magnet even in the axial gap motor in the same manner as that of the radial gap motor. Further, in both of the peripheral opposing case and the surface opposing case, the disc is rotated by the rotating turn table 34 so as to function as the disc apparatus.
There have been problems mentioned below in the conventional motors structured in the manner mentioned above. That is, the conventional radial gap motor has a motor operating principle of utilizing the magnetic suction force and the repulsive force between the N and S poles in the magnetic field system and the protruding pole of the armature (core) so as to rotate. That is, the suction and the repulsion are repeated during one cycle of the motor. This repeat inherently generates a torque change and an uneven torque. With respect to the uneven torque, an uneven torque portion with respect to a total torque is called as a cogging. On the basis of the operating principle mentioned above, it is normally considered that the radial gap motor can not avoid the cogging generated together with the rotation.
Further, in the conventional axial gap motor, since the structure is made such that the yoke, the coil circuit board and the rotor magnet are laminated in the axial direction, a limitation exists in making the structure thin. Further, due to the arrangement of the coil circuit board and the structure of the coil, it is disadvantageous in comparison with the motor having the peripheral opposing structure in view that the large torque is generated.
In particular, in the equipment using a compact disc, a motor having a more compact size and capable of generating a strong torque is required for the purpose of having a good use of the compact characteristic. The present invention is made by solving the problems mentioned above, and an object of the present invention is to provide a motor which can reduce a generation of a cogging, has a thin size, and can generate a strong torque.